Technical Field
The present invention generally relates to storage tanks, specifically, septic tanks, and their construction. More particularly, the present invention relates to septic tanks comprising internal plastic vessels encased by concrete, and their fabrication, and to devices and methods for retaining the shape of an internal plastic vessel of a septic tank while the vessel is encased with concrete.
Description of Related Art
In the design and construction of underground storage tanks, for example, septic tanks, for commercial or residential use, some of the design considerations include 1) preventing leakage of effluent from the tank or seepage into the tank; 2) minimizing or preventing buoyant displacement of the tank, for example, due to ground water; and 3) structural integrity, especially when the tank is expected to be exposed to traffic loading, such as, truck traffic.
Previous attempts to address these design concerns have varied, and, for the most part, have been unacceptable. For example, existing prior art “plastic tanks” when used for underground storage can be effective in preventing leakage and seepage, but underground plastic tanks are prone to buoyancy when exposed, for example, to ground water, and can be lifted and otherwise displaced by buoyant forces. In addition, plastic tanks (and non-plastic or metallic tanks) that are exposed to fluctuating loading, for example, during repeated fill and “pump out” may fail. For example, with the release of hydrostatic load during removal of the vessel's contents, the external loading on the walls of the tank (including ground water loading) may cause the vessel to collapse under the external load. Moreover, plastic tanks typically cannot provide the structural strength to withstand traffic load, for example, when the underground plastic (or non-plastic) storage tank is located under a roadway, such as, a driveway.
In contrast, existing prior art “concrete tanks” can provide the structural strength and, typically, are not buoyant, but cannot ideally prevent leakage. Over time, porous concrete structures can allow the contents of the tank to undesirably leak into the surrounding ground, and possibly, to adjacent ground water or to adjacent bodies of water. Porous concrete structures may also be susceptible to seepage into the structure by groundwater, for example, as the water table raises and falls.
Existing concrete storage tanks, for example, concrete septic tanks, can also be prone to attack and deterioration by bacteria. Due to this, potential, concrete tanks are often at least partially coated with a tar-like material to prevent the growth of bacteria and the deterioration of the concrete. This treatment of, for example, the internal surfaces of septic tanks can be cumbersome, time consuming, and expose the service technician to an undesirable gaseous atmosphere, typically requiring ventilation or the use of a respirator.
Accordingly, there is a need in the art for a storage vessel, in particular, an underground storage tank, such as, a septic tank, that can overcome the limitations and disadvantages of the prior art. Aspects of the present invention address the potential deflection of vessels when exposed to external loading, such as, hydrostatic or fluid concrete loading, during fabrication.